Computers can be programmed to perform many types of important functions. Frequently, the programming is implemented as numerous software components that interact to yield a desired behavior for the computer.
The software components may be initially stored in some form of non-volatile memory, such as a hard disk. Such memory can provide persistent storage for a large amount of computer software and data used in operating a computer.
However, a conventional computer system traditionally does not execute software components directly from non-volatile memory. The non-volatile memory may be too slow to allow access to instructions and data as the computer operates. Accordingly, a conventional computer may “load” software components before they are executed so that they can use fast memory.
Frequently, some software is loaded each time a computer is powered up. However, not all software is loaded at power up. A computer may be programmed with more software than is used at one time. Accordingly, it is known to dynamically load software components. These components are stored as a file containing computer-executable instructions in a form that can be executed without compiling. These files also may be called “binaries” or “executables.”
Loading is done by a component of an operating system, called a “loader.” The loader performs multiple operations that are needed to make a binary ready for execution, including allocating fast memory to store computer-executable instructions that make up the binary. The loader may also trigger allocation of fast memory to store data accessed by the binary.
A binary may implement multiple functions, sometimes referred to as a library of functions. The functions implemented in a binary may be defined in an “interface contract.” The interface contract defines application programming interfaces (APIs) that can be used to access the functions in the library. Other components may be said to “consume” the interface contract. Once the binary is loaded, the consuming components can access, or link to, all of the functions in the library by accessing the functions using interfaces defined in the interface contract. For this reason, a software component that is loaded in this fashion may be called a “dynamically linked library.”
Because the interface contract for a component is known in advance, components consuming the interface contract can be written using APIs defined by that contract so that they can interact with the library. Each dynamically linked library may include an import address table that identifies other dynamically linked libraries that it consumes, which are sometimes referred to as dependent dynamically linked libraries. When one dynamically linked library is loaded, a loader may load the dependent binaries for that library. Though, a loader may defer loading dependent binaries until a later time, such as when the dependent binaries are actually accessed.